Locking and unlocking nut structure

A locking and unlocking nut structure comprising:

• a body including a through hole passing therethrough axially, a diameter of the through hole being larger than that of a screw rod, the body also including a semi-circular recess defined on a top surface thereof, and the semi-circular recess having a starting segment defined on one end thereof and a stopping segment defined on another end thereof, the body further including a slot formed around an upper end thereof relative to the semi-circular recess and a diameter-decreased screw section defined on the inner wall of the through hole thereof opposite to the stopping segment of the semi-circular recess;
• a slidable block formed in a C shape and retained in the semi-circular recess and guided by the slot to move between the starting segment and the stopping segment of the semi-circular recess, the slidable block including first threads defined on one of two outer surfaces thereof, while the slidable block is fixed on the starting segment of the semi-circular recess, a distance from the first threads of the slidable block to an inner wall of the through hole is larger than an outer diameter of the screw rod;
• while the slidable block is fixed on the stopping segment of the semi-circular recess, a distance from the first threads to the diameter-decreased screw section of the through hole is equal to the outer diameter of the screw rod;
• the screw rod including second threads to match with the diameter-decreased screw section and the first threads of the slidable block.